Soil priming effects following biochar incorporation - International ...

Soil priming effects following
biochar incorporation
Yu Luo 1,2 , Mark Durenkamp 1
Qimei Lin 2 and Phil Brookes 1
1
Department of Soil Science, Rothamsted Research, Harpenden, UK
2
China Agricultural University, Beijing, China

Carbon sequestration
Biochar
Soil Organic C
Soil Organic C
biochar contributes to
the refractory soil
organic carbon pool
help decrease the
effects of global
warming.

The priming effects following
substrate addition
CO 2 CO 2
substrate
Soil Organic C
soil organic C
mineralisation increased
or decreased by the
addition of organic
substrates.
positive priming effects (PE).
Negative PE.

The priming effects following biochar addition
CO 2 CO 2 CO 2
Biochar C
How about biochar?
?
Biochar
Soil Organic C
Positive PE may partially
offsets the effects of
biochar as a long-term
carbon sink in soil
Negative PE could benefit
It still remain poorly understood.

Experimental design
• Soil: Hoosfield pH 4 and pH 8
• Biochar: Miscanthus produced at 350 and 700 o C
• Biochar rate: 50 g C kg -1 soil
• Incubation: 90 and 180 days at 40 % Water
Holding Capacity at 25 °C

pH
8.5
7.5
6.5
5.5
4.5
3.5
0 20 40 60 80 100 120 140 160 180 200
Distance (m)
Site: Hoosfield acid strip
HOOSFIELD ACID STRIP
Started more than 100years ago
pH 8.0
pH 5.0
pH 4.0
Organic C (%)
1.05
1.00
0.95
0.90
0.85
0.80
0.75
0.70
0.65
flinty silty clay loam (18-27 % clay)
0 20 40 60 80 100 120 140 160 180 200
Distance (m)

Experimental design
• Soil: Hoosfield pH 4 and pH 8
• Biochar: Miscanthus produced at 350 and 700 o C
• Biochar rate: 50 g C kg -1 soil
• Incubation: 90 days at 40 % Water Holding
Capacity at 25 °C

Experimental design
• Soil: Hoosfield pH 4 and pH 8
Soil Biochar Treatments
pH4 Nil pH4
• Biochar: pH4 Miscanthus BC350 produced at pH4+BC350
and 700 o C
pH4 BC700 pH4+BC700
• Biochar rate: 50 g C kg-1soil
pH8 Nil pH8
pH8 BC350 pH8+BC350
• Incubation: pH8 90 days BC700 at 40 % Water pH8+BC700 Holding
Capacity at 25 °C

soil organic C loss after 90 days
1000
900
800
µg CO 2-C 2 g -1 soil
700
600
500
400
300
?
?
200
100
?
?
0
pH 4 pH 4 +
biochar
350
pH 4 +
biochar
700
pH 8 pH 8 +
biochar
350
pH 8 +
biochar
700

Quantification of CO 2 evolution
δ 13 C
C3-Soil pH 4 -26.579
pH 8 -26.946
C4-Biochar BC350 -12.002
BC700 -12.291
Based on the different stable isotope composition
(represented as δ 13 C value), the percentage of CO 2 -C
from C4 plant can be known by determining the carbon
isotopic composition after incorporation of new C4
vegetation C in C3 SOM pools.

Quantification of CO 2 evolution
µg CO 2-C 2 g -1 soil
900
800
700
600
500
400
300
200
100
soil-derived CO2
biochar-derived CO2
PE
PE
PE
PE
0
pH 4 pH 4 +
biochar
350
pH 4 +
biochar
700
pH 8 pH 8 +
biochar
350
pH 8 +
biochar
700

The Soil organic C loss caused by the priming effects offsets
the positive effects of biochar on carbon sequestration
But…

This loss will be more than compensated
CO 2 CO 2
by biochar incorporation
CO2
Biochar C
biochar loss
SOC loss
Soil Organic C
Soil
Soil
Organic
Organic C
Soil Organic C
With biochar
Without biochar

Organic C in soil after 90 days
7
6
% of C in
soil
5
4
3
2
1
0
pH 4 pH 4 +
BC350
pH 4 +
BC700
pH 8 pH 8 +
BC350
pH 8 +
BC700

Unpyrolyzed
biomass
CO 2 CO 2
CO 2 CO 2
pyrolyzed
biochar
?
Soil Organic C
Soil Organic C
With pyrolysis
Without pyrolysis

Short conclusion
• Biochar caused priming effect, especially with biochar350, thus,
partially offsets the positive effects of biochar on carbon
sequestration
• Priming effects caused by Miscanthus biochar might be smaller
than non-pyrolysed Miscanthus. Also, this C loss might be more
than compensated. Both needs further research.

Correlation between soil organic C mineralisation
and biochar mineralisation
Interactive increased mineralisation between added biochar and soil organic C
was explained as microbial co-metabolism

iological
Soil Organic C
Biochar

Soil ATP after 90 days
ATP nmol g-1 soil
5
4
3
2
1
pH 4
5
4
3
2
1
pH 8
0
0

Soil microbial biomass
200
pH 4
200
pH 8
Microbial biomass C
(µg C g- -1 soil)
150
100
50
150
100
50
0
O 350 700
0
O 350 700
BC350 increase biomass but BC700 doesn’t change
All data represent the mean of 3 replicates +/- SE

Microbial colonization in pH high soil
+BC350
+BC700

Water Extractable Organic Carbon and Nitrogen

Biochar incorporation into Biomass
30
25
20
15
10
5
pH4 pH8
biochar derived
microbial biomass (%)
BC700 in
pH4 soil
0
O + BC350 O + BC700

iological
Soil Organic C
Biochar
Physicochemical

Soil acid properties
K 2 SO 4
extractable Al
K 2 SO 4
extractable Mn
Treatments
Soils
pH
(µg g -1 soil)
(µg g -1 soil)
O Low pH 3.73 (0.02) 540.41 (5.27) 66.30 (1.30)
High pH 7.47 (0.03) 6.63 (2.84) DD
O+biochar350 Low pH 4.41 (0.03) 265.12 (18.0) 105.66 (2.64)
High pH 7.70 (0.02) 3.82 (1.50) DD
O+biochar700 Low pH 5.14 (0.01) 203.98 (10.9) 7.40 (0.07)
High pH 8.06 (0.02) 2.92 (2.12) DD

The mechanisms of short term PE
It may caused by the activated soil microorganisms
through:
Food--labile organic C and nutrient availability
House—large surface area
Better environment--Liming effect

iological
Soil
charsphere
Biochar
Physicchemical

1. Large surface area
2. available C and nutrient
3. Water
4. Temperature
5. Aeration
6. Liming effect
Microorganisms
Soil Organic C
Root
Added OM

Conclusion
Biochar caused short term priming effect, especially with biochar350
The soil organic C loss or surplus with the addition of biochar needs
further investigation.
The priming effects were most probably caused by the activated soil
microorganisms through the water soluble components of the
biochar, or by others, like, surface area, liming effects.
The interaction between different organic C in the charsphere
requires further investigation

Acknowledgements
Jean Devonshire
Wendy Wilmer
Anne Duffy
Martina Masna
-Rothamsted Research, Harpenden, UK
Guitong Li
Xiaorong Zhao
Tao Ma
-China Agricultural University, Beijing, China
CSC funding

The mechanisms of short term PE
Caused by the activated soil microorganisms through:
Food--labile organic C and nutrient availability
House—large surface area
Better environment--Liming effect
Also, possibly, advanced home appliances
a) air conditioner (aeration)
b) Humidifier (moisture)
c) heater (albedo)

appendix
13 C Calculation
ATP,
biomass, methodology

The standard equation for determining δ 13 C (‰) is derived from:
δ 13 C (‰) = [(R sample /R VPDB ) – 1] × 1000, Eqn. 1
where R sample is the mass ratio of 13 C to 12 C and R VPDB is the international PDB
limestone standard.
The labelled 13 C (%) was then estimated from:
CO 2 - 13 C (%) = (δ treatment - δC3) / (δC4 - δC3), Eqn. 2
where CO 2 - 13 C (%) is the proportion of evolved CO 2 from C4 (Miscanthus biochar)
materials, δ treatment is the δ 13 C (‰) in treatment, δC3 is the δ 13 C (‰) in control soil
and δC4 is the δ 13 C (‰) from C4 (Miscanthus biochar) materials.
Thus, the CO 2 -C produced by biochar during the incubation was calculated from:
CO 2 - 13 C (μg g -1 soil) = CO 2 - 13 C (%) × total evolved CO 2 -C (μg g -1 soil) Eqn. 3

The absolute priming effect (or primed soil CO 2 -C) with the addition of biochar was
calculated from:
Primed soil CO 2 -C (µg C g -1 soil) = CO 2 -C treatment - CO 2 -C control , Eqn. 4
where CO 2 -C treatment is the non-isotopically labelled CO 2 -C evolved from biochar
amended soil, CO 2 -C control is non-isotopically labelled CO 2 -C evolved from control.
The priming effect of soil organic C, expressed as the % increase compared to CO 2 -
C evolved from the control was calculated from:
Priming effect (%) = 100 × (CO 2 -C treatment - CO 2 -C control ) / CO 2 -C control Eqn. 5

Plants possessing the C3 pathway have δ 13 C
values with a mean of –27‰.
Plant with C4 photosynthesis discriminate less
Plant with C4 photosynthesis discriminate less
against 13 CO 2 , thus have greater δ 13 C values
than C3 plants, with a mean of –13‰.

Soil microbial biomass--ATP
An independent measure of soil microbial
biomass
Only present in living cells
Linearly related to soil microbial biomass C
May be accurately and precisely extracted
from soil and measured by firefly luciferin –
luciferase reagent.

ATP concentration of microbial biomass
10.4 µmoles ATP g -1 biomass C (n=207)
Contin
et al.
(2001)

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